A relay device is often provided between a server device and a terminal device (a client device) to increase communication rates and safety. Communication data are often encrypted to further increase communication safety. With regard to a combination of such a relay device and encryption of communication data, several techniques have been suggested.
For example, in a communication method described in PTL 1, a secure sockets layer (SSL) proxy server, which relays communications between a web server and a terminal, issues a proxy certificate, based on a server certificate from the Web server and transmits the proxy certificate to the terminal.
In addition, a relay processing device described in PTL 2 performs an SSL handshake with an information processing device (a server device) to acquire a public key certificate of the information processing device from the information processing device before establishing an SSL communication with the information processing device. Then, the relay processing device transmits the public key certificate of the information processing device to a client terminal using a controlled communication at some point between starting the SSL handshake for establishing an SSL communication with the client terminal and actually establishing an SSL communication with the client terminal.
Further, in an encrypted communication system described in PTL 3, when transmitting a request for establishing an encrypted communication path to a server, a terminal transmits the request by specifying a relay device that is permitted to decrypt the request in the middle. The specified relay device establishes an encrypted communication path individually with an adjacent terminal, relay device, or server.